The Phylum Arthropoda is the largest phylum in the Animal Kingdom, which includes insects. Over two-thirds of all named species on Earth are arthropods. These creatures are found everywhere—from deep oceans to high mountains! Understanding arthropods is crucial for competitive exams like SSC, RRB NTPC, UPSC, and state-level exams.
In this guide, we will explore the key features, classification, and examples of arthropods in a simple and easy-to-understand manner.
What is Phylum Arthropoda?
The word Arthropoda comes from two Greek words:
- Arthro = Jointed
- Poda = Legs
Thus, Arthropoda means “jointed legs.”
Arthropods make up about 80% of all known animals on Earth. They are the most diverse and widespread group of animals.
Key Characteristics of Arthropoda
Arthropods have some unique features that make them different from other animals:
- Body Segmentation – The body is divided into three parts:
- Head
- Thorax
- Abdomen
- Exoskeleton – They have a hard outer covering called the chitinous exoskeleton, which protects their body and provides support.
- Jointed Appendages – Their legs, antennae, and other body parts are jointed, which helps in movement.
- Bilateral Symmetry – The left and right sides of their body are equal.
- Triploblastic and Coelomate – They have three germ layers and a well-developed body cavity.
- Open Circulatory System – Their blood does not flow in closed blood vessels but moves in an open cavity.
- Respiration – They breathe through gills, book gills, book lungs, or tracheal system, depending on their habitat.
- Sensory Organs – They have antennae, eyes (compound and simple), and statocysts (balancing organs).
- Excretion – It occurs through Malpighian tubules.
- Reproduction – They are mostly dioecious (separate sexes). Fertilization is usually internal. Most species are oviparous (egg-laying). Development may be direct or indirect.
Classification of Arthropoda
Arthropods are classified into four major classes:
1. Class – Insecta (Insects)
- The Body is divided into the head, thorax, and abdomen.
- Have six legs (three pairs).
- Examples: Butterflies, Ants, Grasshoppers, Mosquitoes
2. Class – Arachnida (Arachnids)
- The Body is divided into cephalothorax and abdomen.
- Have eight legs (four pairs).
- Examples: Spiders, Scorpions, Ticks
3. Class – Crustacea (Crustaceans)
- Mostly live in water.
- Have two pairs of antennae.
- Examples: Crabs, Lobsters, Prawns
4. Class – Myriapoda (Centipedes & Millipedes)
- Long, segmented body with many legs.
- Centipedes have one pair of legs per segment (fast-moving).
- Millipedes have two pairs of legs per segment (slow-moving).
- Examples: Centipedes, Millipedes
Differences Between Insects, Arachnids, and Crustaceans
| Feature | Insects | Arachnids | Crustaceans |
|---|---|---|---|
| Legs | 6 (3 pairs) | 8 (4 pairs) | Varies |
| Body Parts | Head, thorax, abdomen | Cephalothorax, abdomen | Cephalothorax, abdomen |
| Antennae | 1 pair | None | 2 pairs |
| Habitat | Land | Land | Mostly water |
| Examples | Butterfly, Ant | Spider, Scorpion | Crab, Lobster |
Economically Important Arthropods
Useful Arthropods
- Apis (Honey bee) – Produces honey and wax.
- Bombyx (Silkworm) – Used for silk production.
- Laccifer (Lac insect) – Produces lac (used in varnish).
Harmful Arthropods
- Vectors (Disease carriers) – Anopheles, Culex, and Aedes (mosquitoes cause malaria, filariasis, and dengue).
- Gregarious Pests – Locusta (Locust, known for destroying crops).
- Living Fossil – Limulus (King Crab, an ancient species).
Importance of Arthropods
- Pollination – Insects like bees help in pollinating flowers.
- Decomposers – They break down dead plants and animals.
- Food Source – Crustaceans like crabs and prawns are eaten worldwide.
- Silk Production – Silkworms help in making silk.
- Harmful Effects – Some arthropods are pests (termites, mosquitoes) and cause diseases (malaria, dengue).
Fun Facts About Arthropods
- Beetles make up 40% of all insects.
- Spiders produce silk that is stronger than steel.
- Some crabs can live both in water and on land.
- Dragonflies can fly backward!
Conclusion
Arthropods are an essential part of nature and have a huge impact on the environment. Understanding their characteristics, classification, and importance will help you answer competitive exam questions accurately.
Keep learning, stay curious, and you’ll surely succeed! 🚀
Practice Questions
- What is the meaning of the term Arthropoda?
- Name the four main classes of Arthropoda.
- How many legs do insects, arachnids, and crustaceans have?
- Give two examples of each class of Arthropoda.
- What is the function of the exoskeleton in arthropods?
- Name two economically important insects and their uses.
👉 Try answering these questions and test your knowledge!
